Passing pointers of vectors with structures C++

Question

I've declared the following function in C++

void setCellInfo (CELL_MESH* target, int Global_ID, int node0,vector<NODE_MESH *>* NodeStore, vector<CELL_MESH *>* CellStore) {

    CellStore->push_back(target); //No Errors
    target->Global_ID = Global_ID; //No Errors
    
    if (node0 != 0) {
        target->node[0] = NodeStore[vector<NODE_MESH *>::size_type(node0)]->ID; //ERROR 1
        target->node_pointers[0] = NodeStore[vector<NODE_MESH *>::size_type(node0)]; //ERROR 2
    }
}

ERROR1: Gives me a "No member named 'ID' in 'std::vector<NODE_MESH *>'" for the target->node[] attributions although its the entities from the pointers within the vector that have this ID member. Since I'm trying to get a specific entity in the vector using NodeStore[value], I would think it would work.

ERROR2: Gives me "Assigning to 'NODE_MESH *' from incompatible type 'vector<NODE_MESH *>'" for all the target->node_pointers attributions. This seems to be the same problem but with pointers directly (without the ID member).

the NodeStore and CellStore vectors a defined as follows outside the function

vector<NODE_MESH*> NodeStore;
vector<CELL_MESH*> CellStore;

I then try to use the function like this, with 'i' being the int Global_ID and 'nodes_x*y+x' being some integer.

CELL_MESH *newCell = new CELL_MESH;

setCellInfo (&newCell, i, nodes_x*y+x, &NodeStore, &CellStore);

I've tried many different alterations to pointers but can't get it work. Would you know how to ?

Here's a simplified complete version:

#include <vector>

using namespace std;

typedef struct NODE_MESH{
    int ID;
}NODE_MESH;

typedef struct CELL_MESH{
    int Global_ID;
    NODE_MESH* node_pointers[4];
    int node[4];
}CELL_MESH;

vector<NODE_MESH*> NodeStore;
vector<CELL_MESH*> CellStore;

double nodes_y = 5;
double nodes_x = 4;
int cells_y = 4;
int cells_x = 3;

void setCellInfo (CELL_MESH* target, int Global_ID, int node0,vector<NODE_MESH *>* NodeStore, vector<CELL_MESH *>* CellStore) {

    CellStore->push_back(target); //No Errors
    target->Global_ID = Global_ID; //No Errors
    
    if (node0 != 0) {
        target->node[0] = NodeStore[vector<NODE_MESH *>::size_type(node0)]->ID; //ERROR 1
        target->node_pointers[0] = NodeStore[vector<NODE_MESH *>::size_type(node0)]; //ERROR 2
    }
}

int main() {
    
    int i = 0;
    
    for (double y = 0; y < nodes_y; y++) {
        for (double x = 0; x < nodes_x; x++) {
            NODE_MESH *newNode = new NODE_MESH;
            NodeStore.push_back(newNode);
            newNode -> ID = i;
            i++;
        }
    }
    
    i = 0;
    
    for (int y = 0; y < cells_y; y++) { //nodes_y since horizontal faces are aligned with nodes horizontaly (same y)
        for (int x = 0; x < cells_x; x++) { //x coordinate for horizontal faces is in-between nodes so 0.5 with count for faces
            
            CELL_MESH *newCell = new CELL_MESH;
            
            setCellInfo (newCell, i, nodes_x*y+x, &NodeStore, &CellStore);
            
            i++;
            
        }
    }
    
    return 0;
}

Answer 1

Given a variable T* t, the syntax t[x] is equivalent to *(t+x), which is the cause of this confusion. Concretely, NodeStore[vector<NODE_MESH *>::size_type(node0)] is of type vector<NODE_MESH *>& instead of an element of the NodeStore as you expected.

Change your code to take variables by reference instead:

void setCellInfo (CELL_MESH* target, int Global_ID, int node0,vector<NODE_MESH *>& NodeStore, vector<CELL_MESH *>& CellStore) {

    CellStore->push_back(target); //No Errors
    target->Global_ID = Global_ID; //No Errors
    
    if (node0 != 0) {
        target->node[0] = NodeStore[node0]->ID;
        target->node_pointers[0] = NodeStore[node0];
    }
}

The call is then simply

setCellInfo (&newCell, i, nodes_x*y+x, NodeStore, CellStore);

Alternatively, you will need to dereference the pointer before indexing:

(*NodeStore)[node0]->ID